The materialist critics argue that insuperable difficulties are encountered by the hypothesis that immaterial mental events such as thinking can act in any way on material structures such as neurons of the cerebral cortex, as is diagrammed in Fig. 8. Such a presumed action is alleged to be incompatible with the conservation laws of physics, in particular of the First Law of Thermodynamics. This objection would certainly be sustained by 19th century physicists and by neuroscientists and philosophers who are still (...) ideologically in the physics of the 19th century, not recognizing the revolution wrought by quantum physicists in the 20th century. Unfortunately it is rare for a quantum physicist to dare an intrusion into the brain-mind problem. But in a recent book the quantum physicist Margenau (1984) makes a fundamental contribution. It is a remarkable transformation from 19th century physics to be told (p. 22): "that some fields, such as the probability field of quantum mechanics carry neither energy nor matter." He goes on (p. 96) to state: "In very complicated physical systems such as the brain, the neurons and sense organs, whose constituents are small enough to be governed by probabilistic quantum laws, the physical organ is always poised for a multitude of possible changes, each with a definite probability; if one change takes place that requires energy, or more or less energy than another, the intricate organism furnishes it automatically. Hence, even if the mind has anything to do with the change, that is if there is a mind-body interaction, the mind would not be called upon to furnish energy." In summary (p. 97) Margenau states that: "The mind may be regarded as a field in the accepted physical sense of the term. But it is a nonmaterial field; its closest analogue is perhaps a probability field. It cannot be compared with the simpler nonmaterial fields that require the presence of matter (e.g. gravity) nor does it necessarily have a definite position in space. And so far as present evidence goes it is not an energy field in any physical sense, nor is it required to contain energy in order to account for all known phenomena in which mind interacts with brain". In formulating more precisely the dualist hypothesis of mind-brain interaction, the initial statement is that the whole world of mental events (World 2) has an existence as autonomous as the world of matter-energy (World I ) (Fig. 1). The present interactionist hypothesis does not relate to these ontological problems, but merely to the mode of action of mental events on neural events, that is of the nature of the downward arrows across the frontier in Fig. 8. Following Margenau (1984) the hypothesis is that mind-brain interaction is analogous to a probability field of quantum mechanics, which has neither mass nor energy, yet can cause effective action at microsites. More specifically it is proposed that the mental concentration involved in intentions (Figs. 7, 8) or attention (Fig. 4) or planned thinking (Figs. 5, 6) can cause neural events by a process analogous to the probability fields of quantum mechanics. -/- We can ask: what neural events could be appropriate recipients for mental fields that are analogous to quantal probability fields? Already we may have the answer in recent discoveries on the nature of the synaptic mechanism whereby one nerve cell communicates with another. (shrink)